By means of arc-assisted laser welding and with the addition of Al-12%Si welding wire, the butt welding-brazing experiment of dissimilar metals joining aluminum alloy to galvanized steel sheet with filler powder is conducted. The influence of wire feeding speed on weld appearance is discussed. The microstructure, fracture morphology, phase composition, and mechanical property of welded joints are investigated by means of optical microscope, scanning electron microscope, X-ray diffractometer, and material testing machine. The results show that under suitable welding parameters and process conditions, a welding-brazing joint with high quality appearances at both front and back sides can be obtained. When the welding speed is fixed, with the increment of wire feeding speed, the spreading width of welds at the front side decreases, while that of the back side increases. Si element enriches mainly in the upper part of joints, and the welded seams consist of α(Al) substrate and Al-Si eutectic phases along grain boundaries. A kind of non-uniform intermetallic compounds is formed in the Al/steel interface layer which consists of Al8Fe2Si, Fe4Al13, and Fe2Al5. The maximum tensile strength of joints is up to 130 MPa, and the surface morphology of fractures possesses a ductile and brittle hybrid characteristic.